The present invention relates to implantable pacing leads generally and more particularly to implantable single pass A-V leads.
Over the years, there have been numerous proposals for single pass leads which can pace and sense in both the atrium and ventricle. As a practical matter, however, the single pass A-V leads available correspond generally to those illustrated in U.S. Pat. No. 4,091,817 issued to Thaler and include atrial electrodes which are in general only effective for sensing atrial depolarizations rather than pacing the atrium. The problem with single pass A-V leads has been the difficulty of providing a workable lead which reliably fixes an atrial pacing electrode adjacent atrial tissue without producing a lead which is unduly large in cross-section or unduly complex in manufacture or use. Examples of single pass A-V leads include leads in which the lead body is pre-formed to display a bend to urge an electrode into contact with the atrial wall. Such leads include those disclosed in U.S. Pat. No. 4,154,247 issued to O'Neill, U.S. Pat. No. 5,628,778, issued to Kruse et al. and U.S. Pat. No. 5,628,779 issued to Bornzin et al. An alternative approach has been to provide a lead in which the atrial lead is advanced out of the ventricular lead or conversely that the ventricular lead is advanced out of the atrial lead, the atrial lead being pre-curved in order to locate it in a desired position. Such leads are disclosed in U.S. Pat. No. 4,136,703 issued to Wittkampf, U.S. Pat. No. 4,458,677 issued to McCorkle et al and U.S. Pat. No. 4,393,883 issued to Smyth.
As an alternative to pre-forming the lead body or a portion thereof to urge the atrial electrode into contact with the atrium, it has also been suggested to provide an active fixation device in conjunction with the atrial electrode in order to maintain the atrial electrode in its desired location. Such leads are disclosed in U.S. Pat. No. 4,402,329 issued to Williams and to U.S. Pat. No. 4,497,326 issued to Curry. In such designs, the fixation device is typically fabricated in such a fashion that it can be located within the lead body during passage of the lead through the vascular system to prevent it from snagging on body tissue. In the Curry and Williams patents, this can be accomplished by providing a socket for receiving the atrial active fixation device within the lead body during its passage. An alternative embodiment is also disclosed in Curry wherein the active fixation device is withdrawable into the lead body during passage through the vascular system. Unfortunately, the mechanisms for shielding the atrial active fixation devices in the Williams and Curry patents substantially complicate both the manufacture of the lead and the implantation of the lead. The expedients adopted in these patents typically also produce a lead body of increased thickness as compared to two individual leads, passed down the same vein.